Standards, draft standards, and guidelines that provide requirements for the assurance of high integrity software are studied. The focus is on identifying the attributes necessary in such documents for providing reasonable assurance for high integrity software, and on identifying the relative strengths and weaknesses of the documents. The documents vary widely in their requirements and the precision with which the requirements are expressed. Security documents tend to have a narrow focus and to be more product oriented, while safety documents tend to be broad in scope and center primarily on the software development process. It is found that overall there is little relationship between the degree of risk and the rigor of applicable standards. Recommendations are provided for a base standard for the assurance of high integrity software.<> View full abstract»

Typical strategies for battery charge regulation and load control in stand-alone photovoltaic (PV) systems are presented. Several charge algorithms (methods of controlling current to the battery) are presented, along with terminology used by the PV industry for battery charge controllers. Information gained from an extensive evaluation of commercially available charge controllers and data collected from tests on PV systems in the field are discussed. An overview of battery performance characteristics needed for the successful design and long-term operation of PV systems is presented with the intent of soliciting feedback on the information presented from the battery industry.<> View full abstract»

The transmission of integrity information using a signal format compatible with the Global Positioning System (GPS) and relayed through a geostationary satellite repeater, which will be critical in achieving high integrity and availability of global navigation by satellite is discussed. The inclusion of navigation repeaters designed to fulfil this function, the next generation of INMARSAT spacecraft, INMARSAT-3 is examined. The global navigation satellite system (GNSS) integrity channel (GIC) will employ pseudorandom codes in the same family as, but distinct from, the codes reserved by GPS. The data format of the basic integrity channel is designed to convey user range error information for 24 to 40 satellites. A closed-loop timing compensation technique will be used at the uplinking Earth station, to make the signal's clock and carrier Doppler variations identical to those that would result from an onboard signal source. Therefore, the INMARSAT-3 satellites will increase the number of useful navigation satellites available to any user, and can also function as sources of precise timing. There is also a possibility that wide area differential corrections can be carried on the same signal.<> View full abstract»

An overview of GPS is provided from the perspective of a magazine editor, with an emphasis on marketplace applications of the technology. Maritime, aviation, and vehicle tracking uses are discussed, focusing growth in the civil sector. Reliability issues and future developments are considered.<> View full abstract»

The theory of operation, practical applications, and technical performance of a Global Positioning System (GPS) receiver designed for urban area use are presented. The receiver tracks as many as eight satellites, or all visible satellites, and uses the signals of the four best satellites to ascertain its location. If visibility of one satellite is blocked, one of the additional satellites can be used to provide continuous navigation. Component-level system design choices are shown to support superior automotive vehicle location performance, including optimum mobile communication with satellites and ground-based relays.<> View full abstract»